linux-kernel - Re: [PATCH v2 2/2] mm/compaction: avoid rescanning pageblocks in isolate

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Date:	Fri, 09 May 2014 08:49:35 -0700
From:	Michal Nazarewicz <mina86@...a86.com>
To:	Vlastimil Babka <vbabka@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>
Cc:	Hugh Dickins <hughd@...gle.com>, Greg Thelen <gthelen@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Vlastimil Babka <vbabka@...e.cz>,
	Minchan Kim <minchan@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH v2 2/2] mm/compaction: avoid rescanning pageblocks in isolate_freepages

On Wed, May 07 2014, Vlastimil Babka wrote:
> The compaction free scanner in isolate_freepages() currently remembers PFN of
> the highest pageblock where it successfully isolates, to be used as the
> starting pageblock for the next invocation. The rationale behind this is that
> page migration might return free pages to the allocator when migration fails
> and we don't want to skip them if the compaction continues.
>
> Since migration now returns free pages back to compaction code where they can
> be reused, this is no longer a concern. This patch changes isolate_freepages()
> so that the PFN for restarting is updated with each pageblock where isolation
> is attempted. Using stress-highalloc from mmtests, this resulted in 10%
> reduction of the pages scanned by the free scanner.
>
> Note that the somewhat similar functionality that records highest successful
> pageblock in zone->compact_cached_free_pfn, remains unchanged. This cache is
> used when the whole compaction is restarted, not for multiple invocations of
> the free scanner during single compaction.
>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
> Cc: Michal Nazarewicz <mina86@...a86.com>

Acked-by: Michal Nazarewicz <mina86@...a86.com>

> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Rik van Riel <riel@...hat.com>
> ---
>  v2: no changes, just keep patches together
>
>  mm/compaction.c | 18 ++++++------------
>  1 file changed, 6 insertions(+), 12 deletions(-)
>
-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +--<mpn@...gle.com>--<xmpp:mina86@...ber.org>--ooO--(_)--Ooo--


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